The present invention relates to a rear-wheel steering apparatus for a vehicle, capable of steering rear wheels in association with front wheels.
In general, a vehicle is turned in its steering direction by steering its front wheels. Recently, however, rear-wheel steering apparatuses have been developed, which steer rear wheels in a direction in phase with the steering direction of the front wheels, thereby improving the driving stability and cornering performance of the vehicle. These apparatuses can also steer the rear wheels in a direction opposite, in phase, to the steering direction of the front wheels, thereby reducing the turning diameter of the vehicle.
In an apparatus disclosed in Japanese Patent Disclosure No. 58-214470, for example, the steering direction of rear wheels is controlled by using a solenoid spool valve as a directional control valve, which operates in accordance with the steering angle of a steering wheel, detected by a steering-angle detector.
However, the solenoid spool valve is expensive and requires use of the steering-angle detector and an amplifier. Therefore, the disclosed apparatus is complicated in construction and high in cost. Meanwhile, the steering direction or steering angle of the rear wheels must be controlled, in accordance with the steering angle of the steering wheel, in a manner such that the rear wheels are steered in phase with and in opposite phase to the front wheels, when the steering angle of the steering wheel is small and large, respectively. Accordingly, a microcomputer or some other complicated control device is needed to operate the solenoid spool valve, thus further increasing the cost of the apparatus.
In an apparatus disclosed in Japanese Utility Model Disclosure No. 60-46376, an oil pressure acting on an actuator for rear-wheel steering is controlled by means of a spool valve, which is actuated by operating the steering wheel. However, this apparatus can steer the rear wheels only in phase with the front wheels, and not in opposite phase. If an external force from the road surface is applied to the rear wheels, moreover, a reaction force acts on the steering wheel, through a hydraulic circuit, thus spoiling the steering feel.